Thanks, Mike. I think we're in solid agreement here. I think there is
no debate that running multiple instances of Derby in the same VM
without hurdles or impact to the user is the holy grail here. Note, by
the way, that the use of system properties is getting in the way even
before shared code gets introduced. Each instance of Derby needs to be
isolatable within its own classloader, including all its configuration,
and that currently doesn't exist.
What I am thinking of is a way to make it so code sharing allows this
without requiring lots of compatibility hoops for the developer to jump
through. If this is not achievable, we'll continue with the
hasFeature() mechanism that exists in the version I posted last week.
But I am starting to hope (although it is still quite likely I am wrong)
there may be a way around this.
I think what I should just do some prototyping and show it to you --
speak with code. I was trying to test the waters before spending a lot
of time on this, but I think my intent will become much more clear with
some code.
David
Mike Matrigali wrote:
Due to the embedded nature of derby, and if it were to become popular I
believe that it may be common for users to wish to run multiple
instances of Derby in the same VM (actually I don't think users will
know anything about it as they will be running some other piece of
software that has chosen Derby so that they could seamlessly run
a database without letting the user know anything about it). I
know with Cloudscape there were cases of at least 4 instances of
Cloudscape in a given JVM, all layered within products that did
not anything about the other pieces of software.
Now we can pile hurdles in front of the users or the applications
embedding Derby and that will work for some number. But any hurdle
will mean less adoption of Derby.
I understand that the compatibility stuff is a pain, but if Derby
can solve it then it make it stand out. Just as the soft/hard
upgrade stuff is a pain to developers but will enable it's use in
some applications that otherwise could not adopt Derby.
David Van Couvering wrote:
Hi, all. I've been reading Kathey's email about her work on a
classloader that can isolate Derby instances (and the trouble she's been
having with system properties), and I'd like to pose something to the
list.
I am thinking (and I think Kathey's thinking along the same lines)
perhaps there is a way to either transparently or with very little work
from the user (e.g. a property on the connection URL) make it possible
to isolate loading of Derby classes using some kind of specialized
classloader.
*If* I can figure something out, this could remove the requirement to
support backward and forward compatibility, which is a serious albatross
right now around shared code.
Is this work that you think is valuable, or am I chasing a red herring
(lots of bird analogies in this email).
Thanks,
David
begin:vcard
fn:David W Van Couvering
n:Van Couvering;David W
org:Sun Microsystems, Inc.;Database Technology Group
email;internet:[EMAIL PROTECTED]
title:Senior Staff Software Engineer
tel;work:510-550-6819
tel;cell:510-684-7281
x-mozilla-html:TRUE
version:2.1
end:vcard
